nodejs mariadb connection not disconnecting

Question

hi I am using nodejs to create a rest API

but I am facing a problem

first see code

var http = require('http');
var url = require('url');
var mariadb = require('mariadb');

    http.createServer(function (req, res) {
        res.writeHead(200, {'Content-Type': 'text/html'});
        var db_conn  = mariadb.createPool({
            host:"localhost",
            user:"root",
            password:"",
            database:"database",
            connectionLimit:1
        });
        db_conn.getConnection().then(db=>{
            db.query("select * from array_languages").then(data => {
                db.end();
                res.write(JSON.stringify(data));
                res.end();
            });
        });
    }).listen(8080,"localhost");

this code is returning the data perfectly.

But every time I make a request the connection is still open despite the request is finished.

Expected Result

Normally what heppens, When ever I execute an script then after execution the MySql connection closes

I have tried to close the connection

by using conn.end()
but connection is still open

I am from PHP Background

In PHP if you request a page, after the execution all the connections will close automatically. but here I am facing something new.

How Can I close The connection after request finish ?